In some medical procedures, a minimally invasive medical device is used to capture or dislodge material from within a patient's vascular system or other body vessel. For example, in certain procedures, balloon catheters are positioned such that the deflated balloon is placed distally of a vascular occlusion. Typically these vascular occlusions are relatively soft, uncalcified deposited along the walls of an artery. The balloon then may be inflated and drawn proximally. This will tend to dislodge any atheromatous material and withdraw it proximally with the balloon. In current procedures, an aspiration catheter will be moved distally into position adjacent the balloon and will be used to aspirate the dislodged material from the vessel.
A number of other minimally invasive surgical procedures are being used to treat vascular occlusions. These procedures include rotational atherectomy and balloon angioplasty. With the increasing use of vascular stents, it has been discovered that tissue or other material may build up inside a stent, reducing the patency of the vessel through the stent. In the course of improving the patency of the blood vessel utilizing these techniques, there is a risk that the material which was formally causing the obstruction within the vessel can simply float downstream with the flow of blood to the vessel. Accordingly, there is an increasing recognition of the value of taking steps to capture the dislodged material.
A number of researchers have proposed various traps or filters for capturing the particulate matter or other embolic particles let loose in such procedures. Some filters are permanently implanted within the vessel. Emboli trapped within the filter are either aspirated out of the interior of the filter or are dissolved using drugs. Other filters are intended to be temporary in nature, typically being removed after the angioplasty, atherectomy or other procedure is complete. Generally, the goal is to retract the filter with the thrombi trapped therein. Unfortunately, many designs of such temporary filters may get relatively difficult or complex to retract the trap back in to the catheter through which it was delivered without simply dumping the trapped thrombi back in to the bloodstream.
One particularly advantageous vascular filter is shown in co-pending U.S. patent application Ser. No. 08/272,425, and International Patent Application No. PCT/US95/08613, which was published as International Publication No. WO 96/01591, the teachings of which are specifically incorporated herein by reference.
FIGS. 11-16 of WO 96/01591 are attached hereto as FIGS. 1-6 of the present application. FIG. 1 is a vascular trap which is suitable for use in temporarily filtering embolic particles and the like from blood passing through a patient's vascular system. This device would most frequently be used to filter emboli from a patient's blood when another medical procedure is being performed, such as by using the trap in conjunction with a rotating cutting blade during an atherectomy, with a balloon catheter during angioplasty, or with a device used to clear the lumen of a stent during a stent cleaning procedure. It is to be understood, though, that the trap could also be used in other similar applications, such as in channels in patient's bodies other than their vascular systems.
The vascular trap 250 of FIGS. 1A and 1B comprises a generally umbrella-shaped basket 270 carried adjacent a distal end of a guidewire 260. The guidewire in this embodiment includes a tapered distal section 262 with a spirally wound coil 264 extending a distal length of the wire. Guidewires having such a distal end are conventional in the art. The basket 270 is positioned generally distally of the coil 264, and is desirably attached to the guidewire approximately with the proximal end of the tapered section as shown in these drawings.
The basket 270 of the device shown in WO 96/01591 (shown in its collapsed configuration in FIG. 1A) includes a distal band 272 and a proximal band 274. The distal band may be made of a radiopaque material, such as gold, platinum or tungsten, and is affixed directly to the shaft of the guidewire 260. This attachment may be made by any suitable means, such as by welding, brazing or soldering. Alternatively, the distal band 272 may comprise a bead of a biocompatible cementitious material, such as a curable organic resin. WO 96/01591 teaches that a radiopaque metal or the like can be imbedded in the cementitious material to increase the visibility of the band for fluoroscopic observation. The proximal band 274 may be formed of a hypotube sized to permit the tube to slide along the guidewire during deployment. The inventors of that prior application suggest that the hypotube be made of a metallic material; a thin-walled tube of a NM alloy should suffice. If so desired, the proximal band may be formed of a more radiopaque metal, or a NM alloy band can have a radiopaque coating applied to its surface.
As taught in some detail in WO 96/01591, the basket 270 taught therein is formed of a metal fabric. The metal fabric of this embodiment is optimally initially formed as a tubular braid and the ends of the wires forming the braid can be attached together by means of the bands 272, 274 before the fabric is cut to length. These bands 272, 274 will help prevent the metal fabric from unraveling during the forming process. (The method of forming the basket 270 is described in great detail in WO 96/01591 and this process is still believed to provide a suitable means for creating such a basket. The process is also discussed briefly below in connection with FIG. 6.).
When the device is in its collapsed state for deployment in a patient's vessel (as illustrated in FIG. 1A), the basket 270 of this device is said to be collapsed toward the axis of the guidewire 260. The distal 272 and proximal 274 bands are spaced away from one another along the length of the guidewire, with the fabric of the device extending therebetween. This publication teaches it is preferred that the basket is in its collapsed engages the outer surface of the guidewire to permit the device to be deployed through a relatively small lumen of a catheter or another medical device.
When the device is deployed in a patient's vascular system, the basket will take on an expanded configuration wherein it extends outwardly of the outer surface of the guidewire. As best seen in FIG. 1B, the shape of the basket 270 when deployed may generally resemble a conventional umbrella or parachute, having a dome-like structure curving radially outwardly from the guidewire moving proximally from the distal band 272. It is to be understood that other suitable shapes could easily perform the desired filtering function, such as a conical shape wherein the slope of the device changes more linearly than the smooth, rounded version shown in FIG. 1B. A relatively flat, disc shape may also suffice, but it is preferred that the device have a cavity or recess (discussed below) to better retain emboli or other material captured thereby. In this expanded configuration, the two bands 272, 274 are closer together, with the distal band 272 optimally being spaced only a short distance from the proximal band 274, as illustrated.
In moving from its collapsed state (FIG. 1A) to its expanded state (FIG. 1B), the metal fabric of this device turns in on itself, with a proximal portion 282 of the collapsed basket being received within the interior of a distal portion 284 of the collapsed basket. This produces a two-layered structure having a proximal lip 286 spaced radially outwardly of the guidewire, defining a proximally-facing cup-shaped cavity 288 of the basket. When blood (or any other fluid) flows through the basket in a distal direction, any particulate matter in the blood, e.g. emboli released into the bloodstream during atherectomy or angioplasty procedures, will tend to be trapped in the cavity 288 of the basket.
WO 96/01591 teaches that the precise dimensions of the metal fabric can be varied as desired for various applications. If the device 250 is to be used as a vascular filter to trap emboli released into the blood, for example, this reference teaches that the pores (i.e. the openings between the crossing metal strands) of the fabric are desirably on the order of about 1.0 mm. These inventors deemed this to be the minimum size of any particles which are likely to cause any adverse side effects if they are allowed to float freely within a blood vessel. They teach that the pores should not be too small, though, because the blood (or other fluid) should be free to pass through the wall of the basket 270. If so desired, the basket may be coated with a suitable anti-thrombogenic coating to prevent the basket from occluding a blood vessel in which it is deployed.
When a fabric having 1.0 mm pores is used to form this basket 270, the forming process reorients the wires relative to one another and in some areas (e.g. adjacent the proximal lip 286) the pores tend to be larger than 1.0 mm. However, because the baskets walls are formed of essentially two thicknesses 282, 284 of the fabric, the effective pore size of the device may be significantly reduced even at these locations.
The device 250 of FIG. 11 is also provided with tethers 290 for collapsing the basket 270 during retraction. The basket may include four independent tether wires, each of which extends proximally from the proximal lip 286 of the deployed basket. The authors suggested, though, that the four tether wires illustrated in the drawings be formed of two longer wires, with each wire extending peripherally about a portion of the proximal lip of the basket. These tether wires may be intertwined with the wires of the metal fabric to keep the tethers in place during use. When such tethers are retracted or drawn down toward the guidewire, the wires extending along the proximal lip of the basket will tend to act as drawstrings, drawing the proximal end of the basket radially inwardly toward the guidewire. This tends to close the basket and entrap any material caught in the cavity 288 of the basket during use so that the basket can be retracted without the use of a cover.
The tether wires 290 may extend along much of the length of the guidewire so that they will extend outside the patient's body during use of the device 250. When it is desired to collapse the basket for retrieval, the operator can simply hold the guidewire 260 steady and retract the tethers with respect to the guidewire. This can tend to be relatively cumbersome, though, and may be too difficult to effectively accomplish without breaking the tethers if the device is deployed at a selective site reached by a tortuous path, such as in the brain.
To address this issue, the authors suggest, as shown in FIGS. 1A and 1B, that the tethers 290 be attached to the guidewire 260 at a position spaced proximally of the basket. The tethers may, for example, be attached to a metal strap 292 or the like and this strap 292 may be affixed to the shaft of the guidewire. When it is desired to close the proximal end of the basket for retraction, they suggest urging an external catheter (not shown) distally toward the basket 270. When the catheter encounters the radially extending tethers, the distal end of the catheter will tend to draw the tethers toward the guidewire as the catheter is advanced, which will, in turn, tend to draw the proximal end of the basket closed.
FIGS. 2A and 2B illustrate an alternative embodiment of the device shown in FIGS. 1A and 1B, also in accordance with the teachings of WO 96/01591. FIG. 2A shows the device collapsed in a catheter C for deployment while FIG. 2B shows the device in its deployed configuration. In FIGS. 2A and 2B, the basket 270 is much the same as that outlined above in connection with FIGS. 1A and 1B. In the embodiment of FIG. 12, though, the distal band 272 is affixed to the guidewire 260′ at the distal tip of the guidewire. The guidewire 260′ is of the type referred to in the art as a “movable core” guidewire. In such guidewires, a core wire 265 is received within the lumen of a helically wound wire coil 266 and the core wire 265 extends distally beyond the distal end of the coil 266. A thin, elongate safety wire 268 may extend along the entire lumen of the coil 266 and the distal end of the safety wire may be attached to the distal end of the coil to prevent loss of a segment of the coil if the coil should break.
In the embodiment of FIGS. 1A and 1B, the proximal ends of the tethers 290 are attached to a metal strap 292 which is itself attached the shaft of the guidewire 260. In FIGS. 2A and 2B, the tethers are not attached to the core wire 265 itself. Instead, the tethers are attached to the coil 266 of the guidewire. The tethers may be attached to the coil by any suitable means, such as by means of laser spot welding, soldering or brazing. The tethers 290 may be attached to the coil 266 at virtually an spot along the length of the coil. As illustrated in these drawings, for example, the tethers may be attached to the coil adjacent the coil's distal end. However, if so desired the tethers may be attached to the coil at a location space more proximally from the basket 270.
An external catheter such as that referred to in the discussion of FIG. 1A, but not shown in that figure, is illustrated in FIGS. 2A and 2B. Once the basket 270 is deployed in a patient's vessel to substantially reach the expanded configuration shown in FIG. 2B and the basket has performed its intended filtration function, the external catheter C can be urged distally toward the basket 270. As this catheter is urged forward, the tethers will tend to be drawn into the distal end of the catheter, which is substantially narrower than the proximal lip 286 of the basket. This will tend to draw the tethers down toward the guidewire and help close the basket, as explained above.
FIGS. 3-5 illustrate yet another alternative embodiment of a vascular trap in accordance with WO 96/01591. This vascular trap 300 includes a basket 320 received over a guidewire 310. In most respects, the basket 320 is directly analogous to the basket 270 illustrated in FIGS. 1-2. The basket 320 includes a proximal band 322 and a distal band 324. As in the device of FIGS. 2A and 2B, the distal band may be attached to the guidewire adjacent is distal end. If so desired, though, a structure such as is shown in FIGS. 1A and 1B, wherein the guidewire extends distally beyond the basket, could instead be used.
As best seen in its collapsed state (shown in FIG. 3), the basket includes a distal segment 325 and a proximal segment 326, with the distal end of the distal segment being attached to the distal band 324 and the proximal end of the proximal segment being attached to the proximal band 322. When the basket 320 is in it expanded configuration (shown in FIG. 4), the proximal segment 326 is received within the distal segment 325, defining a proximal lip 328 at the proximal edge of the device. The wall of the basket thus formed also includes a cavity 329 for trapping solids entrained in a fluid, such as emboli in a patient's blood stream.
The basket 320 of FIGS. 3-5 is also shaped a little bit differently than the basket 270 of the previous drawings. The primary difference between these two baskets is that the basket 320 is a little bit shorter along its axis that is the basket 270. This different basket shape is simply intended to illustrate that the basket of a vascular trap in accordance with the invention can have any of a wide variety of shapes and no particular significance should be attached to the slightly different shapes shown in the various drawings.
In the vascular traps 250 and 250′ of FIGS. 1 and 2, respectively, tethers were used to draw down the proximal end of the basket 270 to dose the basket for retraction. In the embodiment shown in FIGS. 3-5, though, the trap 300 includes a basket cover 340 positioned proximally of the basket 320. The basket cover may also be formed of a metallic tubular braid and is also adapted to be collapsed to lay generally along the outer surface of the guidewire 310. The cover 340 is not directly affixed to the guidewire at any point, though, but is instead intended to be slidabte along the guidewire. As best seen in FIGS. 3 and 4 wherein the cover is In its collapsed state, the cover 340 includes a distal hypotube 342 and a proximal control hypotube 344, with the distal hypotube being attached to the distal end of the cover 340 and the proximal control hypotube 344 being attached to the proximal end of the cover.
The cover 340 is shown in its deployed, expanded configuration in FIG. 5. As shown in that figure, the cover has a similar structure to that of the basket 320, but is oriented to be open distally rather that proximally, as is the basket. As best seen in FIGS. 3 and 4 wherein the cover is in its collapsed state, the cover has a distal segment 352 and a proximal segment 354. When the cover is deployed by urging it distally out of the distal end of the deployment catheter C, the cover 340 will tend to resiliently return to Its expanded configuration and the distal hypotube 342 will slide axially proximally along the guidewire toward the proximal control hypotube 344. This will invert the collapsed cover so that the distal section 352 is generally received within the proximal section 354, defining a distal lip 358 of the cover.
WO 96/01591 teaches that the proximal control hypotube 344 of this cover may extend along a substantial portion of the length of the catheter 310 so that it extends out of the patient's body when the device 300 is in place. By grasping the control hypotube and moving it relative to the guidewire 310, an operator can control the position of the cover 340 with respect to the basket 320, which is affixed to the guidewires. As explained in more detail below in connection with the use of the device 300, once the basket has been deployed and has been used to filter objects entrained in the fluid (e.g. emboli in blood), the cover 340 may be deployed and the trap may be drawn proximally toward the cover by moving the guidewire proximally with respect to the control hypotube 344.
The inner diameter of the distal lip 358 of the cover is desirably slightly larger than the outer diameter of the proximal lip 328 of the basket. Hence, when the basket is drawn proximally toward the cover it will be substantially enclosed therein. The cover will therefore tend to trap any emboli (not shown) or other particulate matter retained within the cavity 330 of the basket. A retrieval sheath S may then be urged distally to engage the outer surface of the cover 340. This will tend to cause the cover to collapse about the basket, tightly engaging the outer surface of the basket. This somewhat collapsed structure can then be withdrawn from the patients channel and removed from the patient's body. By enclosing the basket within the cover, the likelihood of any filtered debris within the basket being lost as the basket is retrieved will be substantially eliminated.
FIG. 6 illustrates the molding element 370 suggested in WO 96/01591 for use in making a basket 270. Although the basket 320 and cover 340 of the trap 300 are shaped somewhat differently, an analogous molding element can be used for these portions of the trap 300 as well by simply modifying some of the dimensions of the molding element 370, but retaining the basic shape and structure of the molding element. It also should be understood that the molding element 370 is merely one possible molding element for forming a shape such as that of the basket 270 and WO 96/01591 teaches a variety of different molding elements and notes that other designs will be apparent to those skilled in the art.
The molding element 370 of FIG. 6 has an outer molding section 372 defining a curved inner surface 374 and an Inner molding section 376 having an outer surface 378 substantially the same shape as the curved inner surface 374 of the outer molding section. The inner molding section 376 should be sized to be received within the outer molding section, with a piece of the metal fabric (not shown) being disposed between the inner and outer molding sections. In a preferred embodiment, the inner surface 374 of the outer molding element and the outer surface 378 of the inner molding section each include a recess (375 and 379, respectively) for receiving an end of the braid. The molding surface of this molding element 370, to which the fabric will generally conform, can be considered to include both the inner surface 374 of the outer molding section and the outer surface 378 of the inner molding section.
WO 96/01591 teaches that the two molding sections 372, 376 are spaced apart from one another and a length of a tubular braid of metal fabric (not shown in FIG. 6) Is disposed between these molding sections. Optimally, one end of the fabric is placed in the recess 375 of the outer molding section and the other end of the fabric is placed in the recess 379 in the inner molding section. As noted above, the ends of the tubular fabric can be clamped prior to this molding process to limit the likelihood that the fabric will unravel. The inner and outer molding sections can then be urged generally toward one another. As the ends of the wire approach one another, the tubular braid will tend to invert upon itself and a surface of the tubular braid will generally conform to either the inner surface 374 of the outer molding section or the outer surface 378 of the inner molding section, arriving at a shape analogous to that of the basket 270 of the traps 250, 250′. The two molding sections can them be locked in place with respect to one another and the metal fabric may be heat treated to set the wires in this deformed configuration.
This published international application also teaches how one may use the traps 250, 250′ and 300 taught therein. It suggests that these traps be deployed for use in conjunction with another medical device and that they will most frequently be retracted from the patient's body after use. WO 96/01591 uses a balloon angioplasty procedure and an atherectomy procedures as contexts for illustrating a method of using such traps. In balloon angioplasty, balloon catheters having inflatable balloons at their ends are positioned within a blood vessel so that the balloon is positioned within a stenosis. These balloons are positioned by tracking the balloon catheter along a guidewire or the like; the balloons typically have a central bore therethrough. Once the balloon is properly positioned, it is inflated and urges radially outwardly against the stenosis. This will tend to squeeze the stenosis against the walls of the vessel, improving patency of the vessel.
When the stenosis is treated in this fashion, though, there is a risk that some debris will break free and enter the blood flowing through the vessel. If left unchecked, this embolus can drift downstream and embolize a distal portion of the vessel. Depending on where the embolus comes to rest, the embolization can result in significant tissue or organ damage. In order to prevent, or at least substantially limit, such embolization, WO 96/01591 suggests the use of a vascular trap 250, 250′ or 300 of with the balloon catheter. The device should be sized to permit it to be passed through the lumen of the particular balloon catheter to be used in the angioplasty.
In one method taught in WO 96/01591, the trap is deployed first. The basket (270 or 320) of the trap is guided to a position located downstream of the desired treatment site through an introduction catheter (e.g. the catheter C in FIGS. 12-15). The basket is then urged distally beyond the end of the catheter, which permits the basket to resiliently substantially return to its expanded configuration from its collapsed configuration within the catheter. Once the trap is in place, the balloon catheter can be exchanged for the introduction catheter, and the balloon catheter can track the guidewire (260 or 310) of the vascular trap. The balloon can then be positioned within the stenosis and expanded, as outlined above. Once the angioplasty has been completed, the balloon can be deflated again and withdrawn proximally out of the patient.
WO 96/01591 also explains that the balloon catheter can be used to perform the same function as performed by the introduction catheter in the preceding embodiment. In this embodiment, the balloon catheter is positioned in the patient's vessel so that the distal end of the balloon catheter is located downstream of the stenosis. The vascular trap (250, 250′ or 300) of the invention is then passed through the lumen of the balloon catheter and the basket is urged out of the distal end of the catheter. The basket will resiliently substantially return to its preferred expanded configuration, whereupon the balloon catheter can be retracted along the shaft of the device's guidewire until the balloon is properly positioned within the stenosis.
If so desired, the balloon catheter can instead be provided with a length of standard catheter extending distally beyond the distal end of the balloon. The balloon can then be positioned within the stenosis and the basket can be urged out of the distal end of the distal extension of the catheter. In such an embodiment, the length of the distal extension of the catheter should be sufficient to properly position the basket with respect to the balloon when the basket exits the distal end of the catheter. This will eliminate the need to perform the separate step of retracting the balloon into position within the stenosis after the basket is deployed. The balloon can then be expanded, deflated and withdrawn as described above.
WO 96/01591 teaches that much the same procedure can be used to deploy a vascular trap for use in an atherectomy procedure. In such procedures, a cutting head is positioned at the distal end of an elongate, hollow shaft and the cutting head has a bore extending therethrough. The trap can be deployed in either of the methods outlined above, but it is anticipated that in most instances the first procedure will be used, i.e. the basket will be deployed with an introduction catheter, which will be removed so that the cutting device can be guided over the guidewire of the vascular trap. This publication also stresses that the device 250, 250′ and 300 could be used in other medical procedures in other bodily channels besides a patients vascular system.
Since the trap is positioned downstream of the stenosis, any debris released during one of these procedures will tend to drift distally toward the basket and be caught therein. In order to prevent any emboli from simply floating past the trap, it is preferred that the proximal lip (288 or 328) of the basket be at least as large as the lumen of the vessel. WO 96/01591 suggests that the natural dimension of the proximal lip (i.e. where the basket has fully returned to its expanded configuration) be made somewhat greater than the vessel's inner diameter so the basket will firmly engage the wall of the vessel.
The method of retracting the basket will depend on which embodiment of the vascular trap is used, namely whether or not the device includes a cover 340. The device 250 or 250′ of FIG. 1 or 2, respectively, do not include such a cover. However, they do include tethers 290 which extend proximally from the proximal lip 288 of the basket to an attachment to the guidewire. In either of these embodiments, a retrieval catheter can be introduced over the guidewire and urged distally toward the basket. As explained above in connection with FIGS. 1 and 2, this will tend to draw the tethers down toward the guidewire, effectively closing the proximal end of the basket 270. Once the basket is sufficiently dosed, such as when the proximal lip of the basket engages the distal tip of the retrieval catheter, the catheter and the vascular trap can be retracted together from the patient's body. By substantially closing the proximal end of the basket in such a fashion, any emboli which are captured in the basket when it is deployed can be retained within the basket until it is removed from the patient's body.
If so desired, a balloon catheter or like device can instead be used, with the balloon catheter being used to draw down the tethers 290 and collapse the basket. The vascular trap can then be withdrawn with the balloon catheter rather than having to separately introduce a removal catheter to remove the trap.
In withdrawing the embodiment illustrated in FIGS. 3-5, the cover 340 is positioned over the proximal lip of the basket before the vascular trap 300 is retracted. Once the medical procedure is completed and any debris has been captured in the basket, the cover 340 is allowed to resiliently substantially return to its expanded configuration. Once it is deployed proximally of the basket, the basket 320 can be drawn proximally toward the cover 340 until it engages or is received within the cover, as noted above in connection with FIG. 5.
In actuality, the cover 340 of FIGS. 3-5 may be unable to return to its full expanded configuration due to the confines of the vessel in which it is deployed. As explained previously, the cover 340 is desirably larger than the basket 320 so that the basket can be received within the cover. However, the basket is optimally sized to engage the walls of the vessel to prevent the unwanted passage of emboli or other debris around the edges of the basket. Accordingly, the distal lip 358 of the cover will engage the wall of the channel before it expands to its full size. The walls of most bodily channels, such as blood vessels, tend to be somewhat elastic, though. The cover 340 will therefore tend to urge harder against the wall of the vessel than the smaller basket and may stretch the vessel a little bit more than will the basket. In this fashion, the cover may still be able to expand to a dimension large enough to permit the basket to be received in the cavity 356 of the cover. If not, the distal lip 358 of the cover can simply be brought into dose engagement with the proximal lip 328 of the basket to generally seal the basket.
Once the cover 340 is brought into engagement with the basket 320, whether by receiving the basket within the cover or, less preferably, by engaging the lips 358, 328 of the cover and the basket, the device can be withdrawn proximally from the patient's vascular system. The cover will tend to prevent any emboli caught in the basket during deployment from being inadvertently lost during withdrawal.
The vascular traps 250, 250′ and 300 shown in FIGS. 1-6 represent a significant advancement over previously available devices. The embodiment of FIGS. 3-5 shows particular promise in that the cover permits the user to withdraw the basket with the emboli entrained therein without having to take any additional precautions to minimize the chances that these emboli will be accidentally dumped back into the bloodstream.